Method for the production of bars in a continuous casting process

ABSTRACT

An improvement in continuous steel casting practice is proposed wherein a cross-sectional temperature equalization of the solidifying bar is brought about by casting the steel in at least two streams into the mould, the stream directed to the mould center to form the core of the cast product having a lower temperature than the stream or streams directed to the outer mould areas to form the marginal zones of the cast product. Depending on the cross-sectional shape of the mould and cast product, respectively, the streams of steel may be supplied from coaxial tundish outlets or from a number of aligned tundish outlets, or else from a plurality of appropriately arranged tundishes, and the difference in the temperatures of the streams may be obtained either by supplying steel from different ladles or by provision of a cooling device along the path of supply of the core-producing central stream steel.

United States Patent n 13,ss3,470

[72] Inventor Friedrich Bohler Seewalchen, Austria (211 Appl. No. 832,702 [22] Filed June 12, I969 {45] Patented June 8, I971 [73] Assignee Verelnigte Osterreichische Elsen-und Stahlwerke Alttlengesellschalt Linz, Austria [32] Priority Aug. 23, 1968 [33] Austria [31] A8229/68 [54] METHOD FOR THE PRODUCTION OF BARS IN A CONTINUOUS CASTING PROCESS 7 Claims, 6 Drawing Figs;

[52] US. Cl 164/82, 164/281 [51] Int. Cl 822d 11/00 [50] Field of Search 164/82, 85, 86, 91, 96, 273, 97-99, 335, 281, 282, 283; 266/38; 18/13 P [56] References Cited UNITED STATES PATENTS 960,372 6/1910 Monnot 164/99X 971,832 [0/1910 Connell l64/9IX 2,993,236 7/1961 Brimley et al.... 18/1 3PX 3,206,808 9/1965 Robinson l64/273X Primary Examiner-J. Spencer Overholser Assistant Examiner-John S. Brown Attorney-Brumbaugh, Graves, Donohue & Raymond ABSTRACT: An improvement in continuous steel casting practice is proposed wherein a cross-sectional temperature equalization of the solidifying bar is brought about by casting the steel in at least two streams into the mould, the stream directed to the mould center to form the core of the cast product having a lower temperature than the stream or streams directed to the outer mould areas to form the marginal zones of the cast product. Depending on the cross-sectional shape of the mould and cast product, respectively, the streams of steel may be supplied from coaxial tundish outlets or from a number of aligned tundish outlets, or else from a plurality of appropriately arranged tundishes, and the difference in the temperatures of the streams may be obtained either by supplying steel from different ladies or by provision of a cooling device along the path of supply of the coreproducing central stream steel.

PATENTEDJUN 8197! 3.583470 sum 1 [1F 3 INVENTOR. FRIEDRICH 80H LER A TTORNEYS.

mama] JUN 8197: 33583470 SHEET 2 OF 3 INVENTOR. FRIEDRICH BOHLER A TTORNEYS.

PATENTED JUN 8K9?! 3.583470 SHEET 3 BF 3 INVENTOR. FRIEDRICH BOHLER wig gu in! (M ATTORNEYS.

METHOD FOR THE PRODUCTION OF BARS IN A CONTINUOUS CASTING PROCESS The invention relates to a method for the production of bars in a continuous casting process, in which steel is cast into a cooled mould and the bar which has formed with a solidified marginal zone is cooled further in a cooling zone following the mould.

It has been known that in continuous casting of iron and steel alloys difficulties arises during solidification which are caused by the fact that during the solidification of the bar the heat is dissipated radially from the interior to the surface. The casting speed has to be kept slow because otherwise the solidified crust of the bar which is formed when the liquid steel is brought into contact with the water cooled mould wall would tear off or break open. In this stage the liquid core of the bar has a relatively large diameter; the heat emission from the liquid core to the solidified surface of the bar is comparatively unsatisfactory.

These difficulties cannot be eliminated by increased cooling at the surface of the bar. If the cooling rate is too great, owing to the great difference in temperature between core and surface, stress cracks will occur causing deficiencies which cannot be eliminated any more during further processing.

Numerous proposals have been made to render the cooling process more uniform and to obtain an improved temperature equalization during solidification. It has been attempted to improve the temperature equalization between the hot core and the solidified outer crust by creating electromagnetic rotary fields, treatment with ultrasonic waves, employing vibration devices and the like, Further it has been proposed to cool the core of the bar by introducing cold material, such as rods, wires and the like, which are fed with the same speed as the cast bar. Finally it has become known to cast a hollow bar which is used as a mould for the central part of a further bar.

Although the art is varied in this field, it has not yet been possible to eliminate these difficulties in a satisfactory manner, partly because the effectiveness of the proposed measures was inadequate, and partly because the apparatuses were too complicated and expensive for practical use.

The aim of the invention is to solve the problem on hand by pursuing a novel path. The invention resides in that the steel is cast into the mould in at least two streams, of which at least one has a lower temperature than the other stream or streams, the stream with the lower temperature being directed into the center of the mould so that it forms the core zone of the continuously cast product.

The temperature of the stream of lower temperature is to be close to the temperature at which the steel is liquefied, while the stream of higher temperature has the normal casting temperature. Since the liquefying temperature of steel lies at about l490 C. and the normal casting temperature between l550 and l570 C., the difference between the temperatures of the stream of lower temperature and the stream of higher temperature amounts to about 60 to 70 C.

For the production of castings with a square or circular cross section the stream with the lower temperature is suitably annularly surrounded by a stream of higher temperature.

The two streams may be combined either before they meet the metal surface in the continuous casting mould or below the metal surface in the continuous casting mould.

Slabs with a rectangular cross section are advantageously produced by directing a stream of lower temperature into the central region of the continuous casting mould and streams of higher temperature on the two sides of the stream of lower temperature into the mould to form the marginal zones of the continuously cast product.

The streams with higher and lower temperature may be supplied from separate ladles holding metal of different temperatures, or from a single ladle, in which case the stream which is to be led into the central region of the mould is cooled by means of inert gaseous cooling agents either on the path between ladle and tundish or between tundish and continuous casting mould.

Furthermore, the invention relates to apparatuses for carrying out such method, According to an embodiment of the apparatus comprising a continuous casting mould, a tundish and two ladles serving to hold steel of different temperature the tundish has two outlets, one of which is annularly surrounding the other, said outlets being formed in that a tube is inserted into a bottom opening of the tundish, the outer diameter of the tube being smaller than the inner diameter of the bottom opening, said tube being connected with the ladle holding the cooler metal, while the hotter metal surrounding the tube and filling the tundish is supplied from the second ladle.

According to another preferred embodiment of the apparatus for the production of slabs, comprising a continuous casting mould, a tundish and a ladle, three outlets are provided in the bottom of the tundish for the formation of three streams, a tubeor gutter-like cooling device having supplies and outlets for a gaseous cooling agent being arranged below the central outlet in the region between the bottom of the tundish and the metal surface in the continuous casting mould. Suitably the tube or the gutter is inclined towards the continuous casting mould.

According to a further embodiment of the apparatus for the production of slabs, two tundishes are provided, one of which has a horseshoe shape and comprises two outlets situated above the marginal region of the mould, while the second tundish with a rectangular shape is arranged between the legs of the first tundish so that its outlet is situated above the central area of the mould.

In order that the invention may be more fully understood the method of the invention and several apparatuses suitable for carrying out such method will now be described with shows a modified embodiment thereof. In FIGS. 5 and 6 an elevation and a plan view of an apparatus for the production of slabs with two tundishes and two ladles are shown.

In FIG. 1 numeral 1 denotes a continuous casting mould, in which the level of the metal surface is denoted by 2. The tundish 3 is arranged above the continuous casting mould, and the two ladles 4 and 5 are positioned above the tundish. These two ladles are bottom tap ladles, the stoppers 8 and 9 serving to open and close the outlets 6 and 7 of these ladles and to control the supply of the liquid metal. The bottom of the tundish 3 has an opening 10 in which a tube 11 is inserted. Tube 11 is connected to the bottom part of the ladle 5. The outer diameter of the tube 11 is smaller than the inner diameter of the opening 10 so that an annular slit 12 is formed. From the ladle 4 liquid metal 14 is led into the tundish and surrounds the tube 11 to a certain height (its level is denoted by 13). The liquid metal 15 from ladle 5, which is fed through the tube 11, has a lower temperature than the metal 14 which is supplied from the ladle 4 and collected in the tundish. At the exit from the bottom opening 10 the hotter metal 14 annularly surrounds the cooler metal I5 and flows together with it in a combined stream into the continuous casting mould 1. When the stream reaches the metal surface 2 in the mould 1, the temperature distribution with an outer hotter marginal zone 17 on the one hand and an inner cooler core zone 16 on the other hand is maintained for some time, although the outer crust begins to solidify on account of the cooling action of the mould. Owing to the kinetic energy of the metal stream a heat exchange takes place in the mould in that the cooler zone in the center expands and the transition from the temperature in the outer zone to the temperature in the core zone becomes smoother.

FIG. 2 shows a modified embodiment of the apparatus according to FIG. 1 in which the tube 11 extends below the metal surface 2 in the mould I. By this provision the metal streams 14 and 15 are not mixed during flow but are kept separate until they reach the metal surface 2. Mixing and temperature equalization can only be achieved in the-mould so that an improved efficiency is obtained.

In FIG. 3 the production of slabs is explained. The apparatus comprises a continuous'casting mould l, a tundish 3 and a bottom tap ladle 4 from which the metal is directed into the tundish. The tundish is provided with three bottom openings 1%, 19 and 20 arranged above the mould in a manner that the stream leaving the bottom opening 19 reaches the central region and the streams 14, 14 leaving the bottom openings 18 and 20 reach the marginal regions of the mould. Below the bottom opening 19, in the region between the underside of the tundish and the metal surface 2, a cooling device 21 is provided which comprises a refractory pipe surrounding the stream 15. The pipe has a supply line 22 and an outlet 23 for an inert gaseous'cooling medium. The gas, which may have a low temperature, is blown in at 22, passes through the circular gap along the stream 15 and escapes through the outlet 23. The stream 15 is cooled in this manner while it proceeds down and similar conditions are created in the mould as in the apparatus according to FIG. 1, Le. a core zone 16 of lower temperature and marginal zones 17 of higher temperature are obtained in the mould. With the apparatus shown in F l0. 3, an appropriate distance between the tundish bottom and the metal surface in the mould is required to obtain an effective cooling of the central metal stream. lt is generally desired to keep the fall height low. This is achieved by a preferred embodiment as shown in FIG. 4 where the central stream 15 is directed under an inclination into the mould. For this purpose an inclined gutter 21 is provided according to FIG. 4 which is covered by a lid 25. The inert gaseous cooling agent is directed through the channel 26 to cool the stream 15. Numeral 27 denotes a baffle wall which is attached to the mould and may have a semicircular cross section. The baffle wall prevents premature mixing of the stream 15 with the metal streams l4, l4.

ln H68. 5 and 6 an apparatus for the production of slabs with two tundishes 30 and 31 is shown. The two tundishes are fed by two ladles (not illustrated), the tundish 31 is supplied with metal of lower temperature than the metal supplied to the tundish 30. The tundish 30 is of horseshoe shape and encloses with its legs one end of the tundish 31 so that the outlets 32 and 32' of the tundish 30 flank the outlets 33 of the tundish 31 and all three outlets are in alignment with each other. The outlet 33 situated above the center of the continuous casting mould has a somewhat larger diameter than the two lateral outlets above the marginal regions of the mould, as is the case with the outlet 19 in the apparatus according to FIG. 3. The dotted curved lines 34 and 35 indicatethe outlines of the two ladles which feed to the tundishes 30 and 31.

What 1 claim is: g d v 1. In a method for the production of bars in a continuous casting process, in which steel is cast into a cooled mould and the bar which has formed with a solidified marginal zone is cooled further in a cooling zone following the mould, the step of casting the steel into the mould in at least two streams, of which at least one has a lower temperature than the other at least one stream, said at least one stream with the lower temperature being directed into the center of the mould so as to form the core zone of the continuously cast product.

2. The method set forth in claim 1, wherein for the production of square and circular cross section cast products the stream with the lower temperature is annularly surrounded by a stream of higher temperature.

3. The method set forth in claim 1, wherein two coaxially directed streams of different temperatures are combined before they meet the steel surface in the continuous casting mould.

4. The method set forth in claim 1, wherein two coaxially directed streams of different temperatures are combined below the steel surface in the continuous casting mould.

5. The method set forth in claim 1, wherein for the production of slabs having a rectangular cross section a stream of lower temperature is directed into the central region of the continuous casting mould and streams of higher temperature are directed on the two sides of the stream of lower temperature into the mould to form the marginal zones of the continuously cast product.

6. The method set forth in claim 1, wherein the streams with higher and lower temperatures are supplied from separate ladles holding steel of different temperatures.

7. The method set forth in claim 1, wherein the streams with higher and lower temperatures are supplied from a single ladle, the stream which is to be led into the central region of the mould being cooled by means of inert gaseous cooling agents on at least one of the paths between ladle and tundish and between tundish and continuous casting mould. 

2. The method set forth in claim 1, wherein for the production of square and circular cross section cast products the stream with the lower temperature is annularly surrounded by a stream of higher temperature.
 3. The method set forth in claim 1, wherein two coaxially directed streams of different temperatures are combined before they meet the steel surface in the continuous casting mould.
 4. The method set forth in claim 1, wherein two coaxially directed streams of different temperatures are combined below the steel surface in the continuous casting mould.
 5. The method set forth in claim 1, wherein for the production of slabs having a rectangular cross section a stream of lower temperature is directed into the central region of the continuous casting mould and streams of higher temperature are directed on the two sides of the stream of lower temperature into the mould to form the marginal zones of the continuously cast product.
 6. The method set forth in claim 1, wherein the streams with higher and lower temperatures are supplied from separate ladles holding steel of different temperatures.
 7. The method set forth in claim 1, wherein the streams with higher and lower temperatures are supplied from a single ladle, the stream which is to be led into the central region of the mould being cooled by means of inert gaseous cooling agents on at least one of the paths between ladle and tundish and between tundish and continuous casting mould. 